How popular is Gustavo?

Gustavo is a very popular first name for males (#418 out of 1220, Top 34%) but a rare last name for all people. (2000 U.S. Demographics)

Gustavo was first listed in 1910-1919 and reached its apex position of #260 in the U.S. in the year 2000, and is at #529 currently. (Top Baby Names, 2015)

Which version is better?

with its source form and related boy names. Gustavus, Gustave, Gustav and Gustaf are the popular related forms of Gustavo (#529 from recent data). Other variants, like Gosta, are seldom used. These relations of Gustavo were popular as baby names during 1880-1889 (median #880) and are now significantly less popular (#1705, 64.9% less usage), with versions such as Gustave becoming somewhat outmoded.